Multi-layer printed circuit boards (PCBs) are commonly used in electronic devices to connect electronic components such as integrated circuits to one another. A typical multi-layer PCB includes many layers of copper, with each layer of copper separated by a dielectric material. Generally, several of the copper layers are used to provide a reference voltage plane or ground plane (“preference planes”). In addition, several layers of the copper are etched to form the lines that connect Individual components (e.g., “traces”). Copper lined through holes (e.g., “vias”) extend though the layers of the PCB to selectively connect the electronic components on the surface of the PCB to the reference planes and traces within the PCB and to selectively connect copper is traces on different layers to one another.
To connect two Integrated circuits, which typically require a high number of traces to be run therebetween, traces are run on several different layers of the PCB. A common approach is to run two signal trace layers between a voltage plane and a ground plane. This four-layer pattern is then repeated as needed to route all the traces between the two Integrated circuits. In this approach one of the signal trace layers is farther from the voltage plane than the ground plane and the other signal trace layer is farther from the ground plane than the voltage plane.
Presently, Integrated circuits are being produced that require signal traces to reference simultaneously both a voltage plane and a ground plane of a processor such as a microprocessor. In addition, these Integrated circuits require that the signal traces have an equal current return path through the voltage plane and the ground plane. In the common approach of running two signal trace layers between a ground plane and a voltage plane, the current return path for signal traces on each layer through the voltage plane and the ground plane is unequal do to unequal spacing between these layers.
A contemplated approach to satisfying the equal current return path requirement, while referencing signal traces to both ground and voltage, is to run a voltage plane between two signal trace layers and to run a separate ground plane next to each of the two signal trace layers. This five-layer approach is thought to satisfy the current return requirement; however, an additional routing layer is needed, thereby increasing production costs, which increase as the number of needed layers increase.
Accordingly, a PCB is needed that is able to satisfy recent current return path and voltage/ground reference requirements without the use of additional layers. The present invention fulfils this need among others.